Meaningful research has been thin on the ground, but a recent study suggests that cutting back on your mileage can yield benefits.
A 2004 study followed marathon runners on a program that involved only three days running per week - a pittance by the standards of many high mileage junkies.
What they found, however, was that even on a three days per week program the runners achieve significant increases in aerobic performance - indeed, of a group of 21 marathon runners they tracked who were running only 3 days per week, 15 achieved personal bests.
So how do you make significant progress on just three days of running per week? The secret is to make every run meaningful.
Most runners include quite a bit of 'junk' mileage in their program. These are easy recovery runs performed between the hard sessions.
Research demonstrates that replacing these junk miles with other activities can provide a significant advantage in terms of recovery.
So use cross training to your advantage - either do an easy bike ride, or go swimming on your non-running days. You'll still be building your endurance base, but will be giving your legs time to recover before the next hard run.